The Clean Air Act requires the sampling of gases, including ambient air and landfill gas, and the analysis of those samples for a variety of volatile organic and inorganic compounds. One problem with the sampling and analysis requirements of the Clean Air Act has been that the required detection limits of volatile organics in gas have often exceeded the capability of existing technology.
For example, gas generated through the decomposition of waste in landfills consists primarily of methane, along with volatile organic compounds. The volatile organic compounds can consist of hydrocarbons, which are relatively inert, or can be halogen compounds containing chlorine, bromine, fluorine, or iodine, which are reactive. In addition, the volatile organic compounds may include aromatic hydrocarbons, such as benzene, toluene, xylene, and the like, which are classified as carcinogenic. The type and concentration of the volatile organic compounds can vary from site-to-site, depending upon the nature of the waste in the landfill.
It has been the practice, in the past, to vent the gas from the landfill. In a typical installation, a number of perforated wells or pipes are distributed throughout the landfill to collect the gas, and the gas is then conducted to a manifold or header for discharge from the landfill. As the landfill gas consists primarily of methane, it has been proposed to use the landfill gas as a fuel for gas aspirated internal combustion engines. The engines can be used at the landfill site for generating electricity or steam, pumping, or other functions. At a typical landfill there may be from two to six engines that are operating on the landfill gas.
The presence of certain volatile organic compounds in the landfill gas, particularly the halogenated compounds, can cause serious problems with operation of the engine. Due to the reactivity of these compounds, they can react with other constituents to form acids which can attack or corrode engine bearings, bushings, valve guides and stems, as well as producing deposits on the valve seats, and deterioration of the engine oil.
Because of these potential problems with the use of landfill gas, it is important to determine the type and concentration of the volatile organic compounds in the landfill gas. If it is found that the landfill gas has a high concentration of volatile organic compounds that could have a deleterious effect on engine operation, steps can be taken to reduce the concentration of the volatile organic compounds by flaring-off the gas for an extended period, or alternatively, treating the gas by catalytic processes to remove or reduce the volatile organic compounds to acceptable limits.
In order to sample and analyze the landfill gas prior to using the gas as a fuel for an internal combustion engine, several methods have been employed under the Clean Air Act.
It has been proposed to collect the landfill gas or ambient air in plastic or metal containers, and ship the containers to a laboratory for analysis, using a standard gas chromatography/mass spectrometry (GC/MS) procedure. However, it has been found that the volatile organic compounds tend to "plate out" on the plastic or metal containers, with the result that the analysis is flawed and results in a lesser and inaccurate determination of the concentration of the volatile organic compounds.
It has also been proposed in the past to sample and analyze the landfill gas or ambient air by a Tenax.RTM. tube method. In this method, a quantity of granular aluminum oxide is contained within a small tube, approximately four inches long, and the landfill gas is fed through the tube, and the volatile organic compounds will be adsorbed on the granular material. The tube is then sealed and shipped or transported to a laboratory for analysis. To analyze the material, the tube is uncapped and the granular material is heated through induction heating to vaporize the adsorbed contaminants, which are then subjected to the standard GC/MS analysis.
The Tenax.RTM. tube sampling method has several disadvantages. First, the sampling method has a relatively short shelf life, in that the volatile organic compounds tend to migrate or desorb from the granular aluminum oxide carrier, so that when the shipping container is opened, the volatilized compounds will escape, so that the resulting analysis is flawed.
Secondly, the Tenax.RTM. tube sampling system is a "one shot" procedure, in which all of the gas released from the granular material on the induction heating is used for a single analysis in the GC/MS procedure. There is no capability of using only a portion of the volatilized gas in order to run additional tests to verify the results.
Further, the Tenax.RTM. tube sampling system also requires that the laboratory have thermal desorption equipment in order to vaporize and release the volatile organic compounds from the Tenax.RTM. material. It has been found that not all analysis laboratories have such equipment.
Therefore, there has been a distinct need for a simple and effective method of accurately sampling and analyzing landfill gas that could be repeated by different laboratories using standard sampling and analytical techniques.